Fluorescence images can be generated in-vivo for imaging of physiological or molecular function in live biological tissues. One exemplary technology that has revolutionized the ways tissue and disease processes can be visualized relates to the use of externally administered fluorescence probes with sensitivity and specificity to certain molecular, cellular or physiological targets. For example, these agents can provide the ability to visualize events that may be difficult to otherwise detect in conventional imaging modes, and when combined with certain detection systems, very high sensitivity or specificity can be achieved. Conventionally, fluorescent light has been used for high-resolution imaging of biological tissue using fluorescence microscopy. For example, a fluorescent light can be emitted from a tissue in response to an excitation light source transmitting excitation light into the tissue. The excitation light can excite the emission of fluorescent light from fluorochromes within the tissue. When using a near infrared light, higher penetration depths can be achieved in comparison to using light in the visible region, and a significant part of optical tissue imaging may be performed in the near-infrared.
Due to recent advances in light source and detection, optical imaging techniques have become increasingly important for the diagnosis and monitoring of disease. Compared with other imaging modalities, optical imaging can provide molecular, functional and anatomical tissue characteristics, originally coming from the interaction of optical radiation with intrinsic tissue or with chromophores and fluorochromes. Certain different approaches, such as, e.g., confocal imaging, multiphoton imaging, microscopic imaging by intravital microscopy and/or total internal reflection fluorescence microscopy can be used for imaging fluorescence in-vivo. However, the prior techniques and systems may not be appropriate for three-dimensional or quantitative imaging of hollow organs, for example, in intra-vascular or gastro-intestinal applications.
Certain near infrared fluorescence catheter systems have been developed for the detecting fluorescence distributions from hollow organs such as the gastrointestinal tract and cardiovascular system. Such systems rely predominantly on surface information from fluorescence reflectance imaging, but likely lack the ability to provide quantitative or three-dimensional information. Such information is important to accurately map the disease, quantify response to therapies, and geographically localize fluorescence signals within target pathology.
An exemplary application of a catheter-based fluorescence imaging technique and systems may be for the detection of atherosclerotic plaques prone to complication (e.g., vulnerable plaques), as it likely remains a need for subjects at risk of myocardial infarction. Molecular imaging of inflammatory processes in atherosclerosis appears promising for detecting high-risk plaques (see, e.g., Jaffer et al. JAMA 2005; JACC 2006; Circulation 2007 in press). Recently, a near infrared fluorescence (NIRF) molecular imaging technique and catheter system have been described to detect inflammation in atherosclerosis using a first-generation intravascular NIRF catheter (see, e.g., Zhu, Jaffer, Ntziachristos et al., J Phys D: Applied Physics 2005). For example, NIRF catheter 10 can be provided which may detect an augmented protease activity in an inflamed atheroma using a protease-activatable NIRF molecular imaging agent, and has been tested experimentally in rabbit aortoiliac atherosclerosis in vivo (n=8 rabbits, as shown in FIGS. 1(a)-1(d)). This exemplary catheter 10 (e.g., 0.017″ shaft/0.014″ tip) may be provided on the same platform as clinically employed Optical Coherence Tomography (OCTî) wires. Due to the relatively low absorbance and autofluorescence in the NIR window, the signal from NIR fluorochromes (e.g., ex/em 750/805 nm) can be detected through blood during catheter pullback 20 as shown in FIG. 1(b). In-vivo saline flushing experiments can show different spectroscopic profiles for plaques compared to the normal vessel wall, and histological analyses reveal strong NIRF signal in cathepsin B-rich and macrophage-rich areas of plaques (see, e.g., Jaffer, Ntziachristos et al. American Heart Association 2006; Chicago, Ill.). In addition, while one exemplary endoscopic Optical Coherence Tomography and Fluorescence Spectroscopy catheter arrangement and technique has been described (see, e.g., Hariri L P, et. al. Lasers In Surgery and Medicine 38:305-313 (2006)), such spectroscopic arrangement/technique does not (a) form images of fluorochrome distribution, (b) utilize the OCT information to effectuate fluorescence imaging, as well as quantitative or three-dimensional images, (c) may not be suitable for intravascular imaging given its large size (e.g., 2.0 mm diameter) and (d) does not address the ability to resolve multiple fluorochromes via multispectral/deconvolution methods described herein.
Further, an intravital catheter-based imaging system (e.g., an angioscope) using geometrical normalization has been considered for molecular imaging in mice (Upadhyay et. al. Radiology 245:523-531 (2007)). However the geometrical size and other aspects of such system did not facilitate its use for intravascular imaging. None of the systems described above however provide the imaging robustness of or teach on hybrid anatomical molecular imaging for offering a highly accurate diagnostic, monitoring or treatment system and importantly for utilizing anatomical information to correct for photon propagation related events in tissue and offer quantitative information that is independent of (a) catheter placement in the hollow organ, b) variation of optical properties that may affect the fluorescence signal and contrast achieved, and c) variation of the depth of the activity that can similarly affect the fluorescence signal and contrast achieved.